Refrigeration
About In every home in America there is a refrigerator. Every 15 minutes or so you hear the motor turn on, and it magically keeps things cold. Without refrigeration, we'd be throwing out our leftovers instead of saving them for another meal. The refrigerator is one of those miracles of modern living that totally changes life. Prior to refrigeration, the only way to preserve meat was to salt it, and iced beverages in the summer were a real luxury. The basic idea behind a refrigerator is very simple: It uses the evaporation of a liquid to absorb heat. In this article, you'll find out how your refrigerator performs its magic based on this simple principle. Parts As we learned in the introduction, the basic idea behind a refrigerator is to use the evaporation of a liquid to absorb heat. You probably know that when you put water on your skin it makes you feel cool. As the water evaporates, it absorbs heat, creating that cool feeling. Rubbing alcohol feels even cooler because it evaporates at a lower temperature. The liquid, or refrigerant, used in a refrigerator evaporates at an extremely low temperature, so it can create freezing temperatures inside the refrigerator. If you place your refrigerator's refrigerant on your skin (definitely NOT a good idea), it will freeze your skin as it evaporates. There are five basic parts to any refrigerator (or air-conditioning system): * Compressor * Heat-exchanging pipes - serpentine or coiled set of pipes outside the unit * Expansion valve * Heat-exchanging pipes - serpentine or coiled set of pipes inside the unit * Refrigerant - liquid that evaporates inside the refrigerator to create the cold temperatures The basic mechanism of a refrigerator works like this: 1. The compressor compresses the refrigerant gas. This raises the refrigerant's pressure and temperature (orange), so the heat-exchanging coils outside the refrigerator allow the refrigerant to dissipate the heat of pressurization. 2. As it cools, the refrigerant condenses into liquid form (purple) and flows through the expansion valve. 3. When it flows through the expansion valve, the liquid refrigerant is allowed to move from a high-pressure zone to a low-pressure zone, so it expands and evaporates (light blue). In evaporating, it absorbs heat, making it cold. 4. The coils inside the refrigerator allow the refrigerant to absorb heat, making the inside of the refrigerator cold. The cycle then repeats. Refrigeration Cycle The refrigerator in your kitchen uses a cycle that is similar to the one described in the previous section. But in your refrigerator, the cycle is continuous. In the following example, we will assume that the refrigerant being used is pure ammonia, which boils at -27 degrees F. This is what happens to keep the refrigerator cool: 1. The compressor compresses the ammonia gas. The compressed gas heats up as it is pressurized (orange). 2. The coils on the back of the refrigerator let the hot ammonia gas dissipate its heat. The ammonia gas condenses into ammonia liquid (dark blue) at high pressure. 3. The high-pressure ammonia liquid flows through the expansion valve. You can think of the expansion valve as a small hole. On one side of the hole is high-pressure ammonia liquid. On the other side of the hole is a low-pressure area (because the compressor is sucking gas out of that side). 4. The liquid ammonia immediately boils and vaporizes (light blue), its temperature dropping to -27 F. This makes the inside of the refrigerator cold. 5. The cold ammonia gas is sucked up by the compressor, and the cycle repeats. By the way, if you have ever turned your car off on a hot summer day when you have had the air conditioner running, you may have heard a hissing noise under the hood. That noise is the sound of high-pressure liquid refrigerant flowing through the expansion valve. Pure ammonia gas is highly toxic to people and would pose a threat if the refrigerator were to leak, so all home refrigerators don't use pure ammonia. You may have heard of refrigerants know as CFCs (chlorofluorocarbons), originally developed by Du Pont in the 1930s as a non-toxic replacement for ammonia. CFC-12 (dichlorodifluoromethane) has about the same boiling point as ammonia. However, CFC-12 is not toxic to humans, so it is safe to use in your kitchen. Many large industrial refrigerators still use ammonia. In the 1970s, it was discovered that the CFCs then in use are harmful to the ozone layer, so as of the 1990s, all new refrigerators and air conditioners use refrigerants that are less harmful to the ozone layer. Basic Maintenance Air Conditioning and Heating Unit Filters: *Filters: Change or clean air filter at least every other month. This will not only help prevent problems with the system and but will also maximize the unit's efficiency and result in savings on the cost of power consumption. If your unit is equipped with a high velocity permanent filter, please vacuum the filter in lieu of replacing it. *Exterior Condenser Unit: Keep exterior compressor unit free of leaves and debris. The exterior coils may be cleaned with a garden hose to help prevent failures. Products/Services Contact Links How refrigerators work? How To Maintain Your Refrigerator Video Category:Physics